4*[x+(40x-4x)/(50+4)]+40[y-(40x-4x)/(50+4)]=40x+4y
4x+(4*36x)/54+40y-(40*36x)/54=40x+4y
-(36²x)/54=36x-36y
-24x=36(x-y)
-2x=3x-3y
5x=3y
x=0.6y
x／4＝[（y－x）／40]+[（y—x—x）／50]
x/4=y/40-x/40+y/50-2x/50
x/4+x/40+x/25=y/40+y/50
50x/200+5x/200+8x/25=9y/200
63x=9y
7x=y
x=1/7y